1. Field
The present invention relates to a method for manufacturing a printed circuit board made by mounting a semiconductor package on a printed wiring board, the printed circuit board, and an electronic apparatus having the printed circuit board
2. Description of Related Art
An electronic apparatus, such as a personal computer and a hard disk drive, has hitherto been provided with a printed circuit board. The printed circuit board is made by mounting a semiconductor package on a printed wiring board. A related-art printed circuit board is manufactured by a manufacturing method disclosed in; for instance, JP-A-2004-79621. In the manufacturing method, a mount process of mounting a BGA (Ball Grid Array) on a printed wiring board having through holes and a filling process of pouring an underfiller into clearance existing between the printed wiring board and the BGA are performed. Before these operations, through holes are sealed with a sealing material, such as an adhesive.
Conventionally, in connection with a printed circuit board, an underfiller is sometimes poured between a semiconductor package and a printed wiring board as in the above-described printed circuit board, in order to enhance reliability of junctions between the semiconductor package and the printed wiring board.
However, in a case where through holes are formed in the printed wiring board, when an underfiller is poured, it might flow out of a back surface of the printed wiring board through the through holes.
In this regard, as in the manufacturing method disclosed in JP-A-2004-79621, outflow of the underfiller to the back surface can be prevented by sealing the through holes with the sealing material.
However, in the manufacturing method described in JP-A-2004-79621, a sealing material must be bonded to a surface on the back (opposite side) of a mount surface on which a semiconductor package is to be mounted, whereby the manufacturing process becomes complex. Further, even when the opposite side of the through holes is sealed, the through holes on the mount surface side are opened, and the inside of the through holes still remains hollow. Hence, intrusion of the underfiller into the through holes cannot be precluded, nor can a wet spread of the underfiller over the mount surface be prevented. Therefore, the underfiller spreads over the printed wiring board more than necessary, which needs an extra underfiller.
JP-A-2004-79621 also discloses sealing of a mount surface of the semiconductor package by a sealing material. However, this technique involves a necessity for using another material for sealing the through holes that is different from the material used for mounting the semiconductor package. This necessity may make manufacturing processes complicate and result in a decrease in the reliability of junctions.
There is also an idea for relocating the through holes to other locations, thereby avoiding overflow of the underfiller. However, it may be difficult to relocate the through holes while ensuring an electrical characteristic of the printed wiring board, in consideration of arrangement of wiring.